Field-effect control power switching structures, e.g. insulated gate bipolar transistors (IGBTs) or field effect transistors (FETs), are present in various semiconductor applications including but not limited to switches in power supplies and power converters.
One example of a field-effect control power switching structure is a vertical structure including a gate electrode in a trench. This vertical structure allows current flow between a first side and a second side of a semiconductor die. At or around a bottom of the trenches, high electric fields may lead to a reduction of a breakdown voltage or even destruction of the semiconductor device. As an example, avalanche occurring in a breakdown mode of the semiconductor device may lead to an unstable behavior of the voltage blocking capability of the semiconductor device due to hot carrier generation. This may even lead to a shift of an electrical breakdown region. In case of IGBTs, dynamic avalanche may lead to undesirable oscillations during device turn off. Thereby, a reliability of the semiconductor device can be adversely effected.
It is desirable to improve the reliability of a semiconductor device.